Some free parking tips:

Monday - Friday: 3-hours of free parking is available all along Ohio Drive SW between the Lincoln and Jefferson Memorials. In the evenings don't worry about the time limit. And don't worry about it on weekends. There's also a small free public parking lot near the Jefferson. Best to do the memorials early morning or evening.

You can park along the Mall for free but would have to get there early in the morning and there is a time limit.

U.S. Capitol Reflecting Pool parking areas -- "Permit Only" signs are not enforced after about 3:00p in the afternoon. No time limit in the evening. This is a great place to park for visiting the U.S. Botanical Garden, Indian, Air & Space, Natural History and National Gallery of Art.

Weekends: The "permit only" signs around the Capitol Reflecting Pool, along Constitution Avenue and D, Delaware and 1st Streets NE are not enforced, at all. Haines Point has free parking on weekends which is fairly convenient to the Holocaust Museum, Jefferson, FDR and Washington Monument. I'm used to walking a lot so "fairly convenient" to me may not be to some others.